Effect-particle orientation and its impact on appearance properties has been the subject of study within the paint industry for many years. Colorimeters and spectrophotometers are well known in the art and are used to measure certain optical properties of various paint films which have been coated over test panels. A spectrophotometer provides for the measurement of the amount of light reflected at varying light wavelengths in the visible spectrum by a painted panel that is held at a given angle relative to the direction of an incident source of light. The reflectance factor of the paint enables paint chemists to calculate color values by which to characterize various paint colors. For a paint containing no light-reflecting flakes or particles, the reflectance factor does not vary with the angle of the panel relative to the direction of the incident light except at the gloss (specular) angle.
Typical effect-particles, for example metallic or pearlescent flakes, mica or other non-spherical particles, are often utilized in paints and coatings to provide a distinctive or appealing appearance because such particles can impact the visual perception of the painted or coated surface. These particles can accentuate the appearance aspects of a substrate such as its curvature, color appearance and color intensity, which may change according to the viewing angle, a desired visual effect for substrates such as automotive panels. Ideally, flat particles provide the greatest change in color per a change in the viewing angles, whereas particles approaching a spherical shape provide the least color change with a change in the viewing angle.
Some continuous sheet and film processes include the use of effect flake particles. However, particle orientation is variable and either not monitored or unable to be monitored, beyond a visual investigation and perspective. This process has been able to achieve a visual effect, but these effects are a result of being imparted in an uncontrolled fashion. It is a very difficult, and somewhat haphazard, method of attempting to match (both visually and color-wise) metallic painted panels and sheet color using pigments and metallic pigments.
In the paint coatings industry using conventional technology, the orientation of the effect-particles is to measure the light reflection at multiple angles in a single determination (i.e., in one direction). The resultant measurement, with a subsequent calculation, provides an indication of the color appearance in a qualitative manner for the specific color being tested. Thus, the color appearance can then be compared and changed or adjusted if necessary. However the use of only a single absolute measurement is problematic because it does not provide a direct determination for identifying when an effect-particle is flat or parallel to a surface. Additionally, the single “flop calculation” method does not provide relative particle orientation suitable for in-process adjustments. Furthermore, outside influences may affect this calculated value, inferring the effect-particles are flat (usually maximizing the “flop” calculation).
Another disadvantage of conventional technology is that the processes known in the art work in a batch-like manner, where the use of a stationary panel having no vibrations is required to provide satisfactory data, and therefore, are too slow to provide adequate control feedback in many continuous processes, particularly plastic sheet processes. As a result, these processes are burdensome, time consuming, not cost effective and thus, not for use with continuous processes.
Thus, it would be desirable to have a process or apparatus capable of taking opposing directional reflectance measurements for an indication of effect-particle orientation in continuous processes, thereby allowing for better control of effect-particle orientation, which is necessary to maintain the appearance consistency of a substrate. Such process or apparatus preferably has the ability to exert greater control over the effect-particle orientation relative to the surface of the effect-particle-containing material as well as controlling the process of the sheet or film melt process, thereby improving the uniformity of sheet polymer orientation. Such process or apparatus provides for greater consistency of appearance when the effect-particle-containing material (e.g. paint, film, coating, coated article or polymer) is viewed at similar angles in opposite directions and between different articles made from the same sheet or film; greater repeatability of particle orientation from one manufacturing campaign to another; and can provide unique orientation characteristics through changing process conditions to provide nearly similar reflection characteristics in opposing directions, or very different reflection characteristics in opposing directions.